The present invention relates to a modified lignin material and to a process for producing said modified lignin material. More particularly, this invention relates to a nitric acid oxidized lignosulfonate composition and to a process for its preparation.
Various and numerous sulfonated and otherwise derived lignin materials have already been found, known and developed and advantageously applied for many useful and beneficial purposes.
Numerous references are available dealing in one way or another with the identity and nature of lignin per se and many of the derivatives of lignin, including lignosulfonates, as well as the preparation and numerous uses of such materials. Substantial information therein can be found by way of illustration in U.S. Pat. Nos. 1,848,292; 2,371,136; 2,371,137; 2,349,183; 2,505,304; 2,576,418; 2,598,311; 2,800,449; 3,087,923; 3,156,520; and 3,726,850. Still additional art of interest is uncovered in U.S. Pat. Nos. RE. 18,268; 2,057,117; 2,104,701; 2,399,607; 2,434,626; 4,181,652; 4,088,640; 4,846,871; 4,065,318; 4,293,459; RE.32,895; 4,752,317; 4,296,813; RE.31,190; and 4,219,471.
Another excellent information source in this area is the bulletin published by Daishowa Chemicals Inc. of Greenwich, Conn. (USA) and Quebec P.Q. (Canada) entitled, "The Lignin Story."
Hoyt U.S. Pat. No. 3,070,591 discloses a process for producing nitric acid oxidized lignosulfonates by admixing a sulfonated lignin material and nitric acid. However, the amount of the nitric acid used is disclosed as being only 1-30% by weight of dry solids of the sulfonated lignin material. As shown herein, an oxidized lignosulfonate produced by such a method is inferior to those produced using higher concentrations of nitric acid.
The lignosulfonates which are preferably utilized as the starting materials in the practice of and to obtain the novel nitric acid oxidized compositions of the present invention are the treated or untreated spent sulfite liquors containing the desired effluent lignosulfonate solids obtained from wood conversion as the sulfite waste pulping liquor. These, as indicated, may be nitric acid oxidized in the "as is" or whole liquor condition. Or and often times with advantage, they may be oxidized as a purified lignosulfonate material from, or in which the sugars and other saccharide constituents have been removed and/or destroyed, or additionally inorganic constituents have been partially or fully eliminated.
Also sulfonated or sulfoalkylated kraft lignin can be used as an adequate raw material for nitric acid oxidation. As used herein, the term "kraft lignin" has its normal connotation, and refers to the substance which is typically recovered from alkaline pulping black liquors such as are produced in the kraft, soda and other well known alkaline pulping operations. The term "sulfonated lignin", as used in the specification refers to the product which is obtained by the introduction of sulfonic acid groups into the kraft lignin molecule, as may be accomplished by reaction of the kraft lignin with sulfite or bisulfite compounds, so that kraft lignin is rendered soluble in water. As used herein, the term "sulfite lignin" refers to the reaction product of lignin which is inherently obtained during the sulfite pulping of wood, and is a principle constituent of spent sulfite liquor. The term "lignosulfonate" (LSO.sub.3) encompasses not only the sulfite lignin, but also the sulfonated lignin herein above described. Any type of lignosulfonate that is hardwood, softwood, crude, or pure may be employed. Preferably, lignosulfonates in their as is or whole liquor condition are employed. For example calcium lignosulfonates, sodium lignosulfonates, ammonium lignosulfonates, modified lignosulfonates and mixtures or blends thereof may all be utilized herein. Lignosulfonates are available from numerous sources in either aqueous solution or dried powder forms. For example Daishowa Chemicals Inc. sells lignosulfonates under the trade designations Lignosol, Norlig, and Marasperse which are appropriate for use in the present invention.
In general, the lignosulfonates are anionic polyelectrolytes with a relative molecular size usually on the order of 1,000 to 20,000 and from which the oxidized products are obtained according to the instant invention. They generally have an organic sulfonic sulfur, that is--SOhd 3, content calculated as percent sulfur by weight of broadly between about 1/2 to about 15 percent. More advantageously for many purposes, this sulfur range is between about 13/4 to about ten percent. While quite often it is preferable for the lignosulfonate to contain from about two to eight weight percent of the combined sulfur which represents its appearance in the sulfonic form.
Many of the lignosulfonates that are advantageously nitric acid oxidized according to the practice of the present invention are obtained in waste pulping liquors derived from a totally or at least substantially hardwood source. However, excellent oxidized lignosulfonate products are also prepared from softwood starting materials.
Good examples of lignosulfonate products of various types which are commercially available from Daishowa Chemicals Inc. include those having the trade designations Norlig and Marasperse. These are generally derived from sulfite waste pulping liquors with Marasperse being considerably refined as to sugars and certain inorganics contents compared to Norlig. The Lignosol products, also available from Daishowa Chemicals Inc., are derived from substantially softwood sulfite waste pulping liquors and can be whole liquor "as is" raw materials or, depending on processing, can be modified or purified softwood lignosulfonates.
While the known lignosulfonate products, including the above mentioned Norlig, Lignosol and Marasperse materials are good surfactant, dispersant, detergent and otherwise attractively propertied materials that are commendable for a wide variety of uses, they still have certain intrinsic inadequacies and limitations leaving some unfulfilled capability for use in many additional applications and for many highly advantageous purposes.